Ultra-High Strength Stainless Alloy Strip, a Method of Making Same, and a Method of Using Same for Making a Golf Club Head

ABSTRACT

A stainless steel strip article is disclosed. The article is formed from a corrosion resistant alloy having the following composition in weight percent, about: 
     
       
         
               
               
               
               
             
                   
                   
               
                   
                 C 
                 0.03 
                 max. 
               
                   
                 Mn 
                 1.0 
                 max. 
               
                   
                 Si 
                 0.75 
                 max. 
               
                   
                 P 
                 0.040 
                 max. 
               
                   
                 S 
                 0.020 
                 max. 
               
               
               
               
             
                   
                 Cr 
                 10.9-11.1 
               
                   
                 Ni 
                 10.9-11.1 
               
                   
                 Mo 
                 0.9-1.1 
               
                   
                 Ti 
                 1.5-1.6 
               
               
               
               
               
             
                   
                 Al 
                 0.25 
                 max. 
               
               
               
               
             
                   
                 Nb 
                 0.7-0.8 
               
               
               
               
               
             
                   
                 Cu 
                 1 
                 max. 
               
                   
                 B 
                 0.010 
                 max. 
               
                   
                 N 
                 0.030 
                 max. 
               
                   
                   
               
           
              
             
             
              
              
              
              
              
             
          
           
              
              
              
              
             
          
           
              
             
          
           
              
             
          
           
              
              
              
              
             
          
         
       
     
     The balance is iron and usual impurities. The elongated thin strip article provides a room temperature tensile strength of at least about 280 ksi in the solution treated and age hardened condition. A method of making the strip article and a method of using it to make a golf club are also disclosed.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional Patent Application No. 61/110,034 filed Oct. 31, 2008, the entirety of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to stainless steel strip material and in particular to a stainless steel strip article having very high tensile strength, a method of making same, and a method of using the strip material for making a golf club head.

2. Description of the Related Art

Golf club manufacturers are constantly looking for a high strength faceplate material. Very high strength allows the faceplate section to be made thinner, and therefore lighter, which provides designers more leeway in club head design. In addition, corrosion-resistant materials are preferable to non-stainless materials because surface coatings or plating, which could be removed during use, are not required.

Current solutions to this problem include the use of standard PH stainless steel alloys such as the CUSTOM 455 alloy and newly designed stainless alloys such as the CUSTOM 465 and CUSTOM 475 alloys. However, the CUSTOM 455 and CUSTOM 465 alloys do not provide the strength levels desired in new club designs. The CUSTOM 475 alloy provides very high strength, but it is also highly alloyed, making it both expensive for the club manufacturer as well as less forgiving in the golf club manufacturing process.

In addition, many club heads are typically manufactured using a cast body with a faceplate. The cast body material is typically formed of a precipitation hardenable stainless steel such as 17-4 PH or 15-5 PH stainless steel. Golf clubs are typically manufactured by welding the faceplate to the cast body and then heat treating the entire assembly to develop final properties. The alloys typically used for the cast body of the club have solution temperatures of about 1900° F., whereas the known faceplate materials have solution temperatures ranging from 1550° F. to 1800° F. This mismatch in heat treating temperatures results in either the club body, or the faceplate material, or possibly both, providing less than optimum properties in the as-heat treated condition after assembly of the club head. In addition, the CUSTOM 475 alloy often requires a different manufacturing process altogether, because the alloy cannot be re-solutioned after club head assembly.

BRIEF SUMMARY OF THE INVENTION

The disadvantages of the known materials are overcome to a large degree by a stainless steel strip article according to this invention. In accordance with the one aspect of the present invention, there is provided a stainless steel strip article that is formed from a corrosion resistant alloy comprising, in weight percent, about:

C 0.03 max. Mn 1.0 max. Si 0.75 max. P 0.040 max. S 0.020 max. Cr 10.9-11.1 Ni 10.9-11.1 Mo 0.9-1.1 Ti 1.5-1.6 Al 0.25 max. Nb 0.7-0.8 Cu 1 max. B 0.010 max. N 0.030 max. and the balance is iron and usual impurities. The elongated thin strip article provides a room temperature tensile strength of at least about 280 ksi in the solution treated and age hardened condition.

In accordance with another aspect of this invention there is provided a method of making a thin strip article. The method comprises the steps of casting a corrosion resistant alloy having the weight percent composition set forth above to form an ingot. The ingot is hot worked to form an elongated strip material. The strip material is then heat treated under conditions of time and temperature to provide an ultimate tensile strength of at least about 280 ksi at room temperature.

In accordance with a further aspect of this invention there is provided a method of making a golf club head. The method includes the step of casting a corrosion resistant alloy having the weight percent composition set forth above to form an ingot. The ingot is hot worked to form an elongated strip article which is then heat treated under conditions of time and temperature to benefit the machinability and processability of the strip material. The strip material is then machined to form a faceplate for a golf club head. The method includes the further step of forming a golf club head body from a corrosion resistant precipitation hardenable steel alloy. The faceplate is bonded to golf club head body. The assembly is then heat treated under conditions of time and temperature sufficient to provide a desired level of hardness and strength in the golf club head body and an ultimate tensile strength of at least about 280 ksi at room temperature in the faceplate.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a graph of tensile strength as a function of aging temperature.

DETAILED DESCRIPTION

A preferred embodiment of the invention includes an elongated strip article having the following composition in weight percent:

C 0.03 max. Mn 1.0 max. Si 0.75 max. P 0.040 max. S 0.020 max. Cr 10.9-11.1 Ni 10.9-11.1 Mo 0.9-1.1 Ti 1.5-1.6 Al 0.25 max. Nb 0.7-0.8 Cu 1 max. B 0.010 max. N 0.030 max. The balance is iron and the usual impurities.

The alloy composition is preferably melted using vacuum induction melting (VIM). The steel is cast into one or more ingot molds. For additional cleanness, the alloy is vacuum arc remelted (VAR) after the VIM step. After solidification, the alloy is formed into strip by intermediate pressing of the ingot to form a billet and then hot rolling the billet to form elongated strip. Alternatively, the strip material can be formed by hot rolling the ingot from a starting temperature of about 1900° F. to 2250° F. The strip can be provided in the overaged condition by heating at about 1100° F. to 1350° F. for about 2 to 8 hours and then cooling in air. Alternatively, and for better machinability and processability, the strip material is heated at about 1900° F. to 1950° F. for about 1 hour, cooled in air, refrigerated at about −100° F. for about 8 hours, and then warmed in air to room temperature. Preferably, the strip material is cold rolled to final or near final thickness prior to being heat treated. The strip material according to this invention can be solution treated in a continuous furnace with times and temperatures adjusted accordingly. For the golf club application, the strip material is processed to a thickness of about 0.02-0.16 inches, preferably about 0.10-0.12 inches.

Unlike the known high strength stainless steel alloys such as the CUSTOM 475 stainless alloy, the alloy strip according to this invention can be double solution treated with no significant loss in properties, particularly no loss of strength. In other words, the stainless steel strip material of this invention can be provided in the solution treated plus refrigerated condition, processed into components, and then re-solutioned, re-refrigerated, and age hardened after being assembled into a golf club head to provide the desired high strength and hardness.

As an example of the elongated strip article according to the present invention, a small heat was melted and processed. The 400 lb heat was melted by VIM+VAR and cast as an 8-inch diameter ingot. The weight percent composition of the VAR ingot is given below in Table I. The balance of the alloy was iron and usual impurities.

TABLE I C Mn Si P S Cr Ni Mo Ti Cb B N Ce 0.005 0.05 0.04 <0.005 <0.0005 11.05 11.02 1.01 1.56 0.79 0.0019 0.0016 0.001

The ingot was homogenized at 2300° F. for 16 hours, and then pressed to a 4-in×8-in billet from a starting temperature of 2000° F. The billet was hot rolled to 7.5 in. wide×0.15 in. thick strip from a starting temperature of 2250° F. The strip was then ground to 0.135 in. thick and then cold rolled to 0.1103 in. thick. The strip was given an overaging treatment by heating at 1146° F. for 5.5 hours. After cooling to room temperature, the strip material was ground to a final thickness of 0.1083 in.

Standard strip tensile blanks were rough cut in the longitudinal and transverse orientations from the overaged strip. Groups of the blanks were solution treated at 1850° F., 1900° F., 1950° F., and 2000° F., respectively, for 1 hour and air cooled. The solution treated blanks were deep chilled at −100° F. for 8 hours and then warmed in air to room temperature. The blanks were then rough machined to provide a gage section about ½ inch wide×2 inches long. Groups of the rough machined blanks from each solution treatment were aged at temperatures ranging from about 900° F. to about 975° F. for 4 hours and then air cooled. The test specimens were finish machined after aging and tested at room temperature.

The results of room temperature tensile and hardness testing are presented in Tables 2-4 below including the solution treatment temperature (Solution Temp.) and the aging temperature (Age Temp.) in ° F., the 0.2% offset yield strength (Y.S.) and ultimate tensile strength (U.T.S.) in ksi, and the Rockwell C-scale hardness (Hardness) as HRC.

TABLE 2 Solution Age Y.S. U.T.S. Hardness Temp. Temp. Orient. (ksi) (ksi) % El. (HRC) 1850° F. 950° F. L 258 266 — 52.0 258 267 — 258 268 — T 260 272 — 260 273 — 245 272 — 975° F. L 244 252 — 50.5 244 253 — 245 253 — T 248 258 — 246 256 — 245 255 —

TABLE 3 Solution Age Y.S. U.T.S. Hardness Temp. Temp. Orient. (ksi) (ksi) % El. (HRC) 1900° F. 900° F. L 260 284 4.8 53.5 261 286 4.3 259 284 4.8 T 264 287 4.3 257 282 2.8 258 285 4.2 925° F. L 259 282 4.0 53.5 257 281 4.2 256 281 4.1 T 247 285 3.9 260 285 4.1 257 285 4.2 950° F. L 250 274 6.2 52.0 252 273 6.7 249 273 6.4 T 251 277 6.5 250 277 6.0 251 276 6.7 975° F. L 234 258 7.3 50.5 235 256 7.1 235 259 6.9 T 243 264 6.8 240 261 6.6 242 263 6.6

TABLE 4 Solution Age Y.S. U.T.S. Hardness Temp. Temp. Orient. (ksi) (ksi) % El. (HRC) 1950° F. 900° F. L * * 4.6 53.5 * * 4.1 * * 4.7 T * * 5.4 * * 4.2 * * 4.8 950° F. L * * 5.3 52.5 * * 5.2 * * 4.3 T 264 275 5.3 267 279 4.9 260 276 5.3 2000° F. 900° F. L 248 282 5.9 53.5 253 283 5.0 255 282 5.5 T 261 286 4.6 258 291 5.1 260 287 4.7 950° F. L 253 276 5.7 53.0 254 277 5.2 255 276 5.2 T 260 281 4.7 261 282 4.6 263 282 5.0 * Strength data was lost for these samples. However, the test operator recalls that the U.T.S. for the H900 samples was above 280 ksi and that the U.T.S. for the H950 samples was slightly under 280 ksi

Metallographic analysis of the test specimens showed that the material solution treated at 1850° F. and 1900° F. had a grain size of about ASTM 8. The material solution treated at 1950° F. had a grain size of about ASTM 7-8. The material solution treated at 2000° F. had a grain size of about ASTM 2-3. Here and throughout this application, the ASTM grain size means average grain size as determined in accordance with ASTM Standard Test Procedure E-112.

The results presented in Tables 2, 3, and 4 show that the preferred solution temperature is about 1900° F. to about 1950° F. Likewise, the preferred aging temperature is about 900° F. to 925° F. in order for the material to provide the desired 280 ksi U.T.S. A graph of U.T.S. versus solution and aging temperature combinations is shown in the drawing.

The data presented in the tables show that a strip article made from the alloy composition described in this application is capable of attaining an U.T.S. 280 ksi or higher. The strip material is much less heavily alloyed than other stainless compositions capable of that strength level, resulting in a lower alloy cost. In addition, the strip material is capable of being solution heat treated more than once without sacrificing strength or toughness properties. The strip material of this invention is preferably solution heat treated at a temperature in range of about 1900-1950° F., making golf club faceplates of this composition fully compatible with the solution treating temperature for the precipitation hardenable stainless casting alloys most often used for the body of golf club head. Therefore, the faceplate and the club head body can be solution treated and age hardened in the assembled configuration to develop maximum hardness and strength, not only in the body of the club head, but also in the faceplate which makes contact with a golf ball.

It will be recognized by those skilled in the art that changes or modifications may be made to the above-described embodiments without departing from the broad inventive concepts of the invention. It is understood, therefore, that the invention is not limited to the particular embodiments that are described, but is intended to cover all modifications and changes within the scope and spirit of the invention as described above and set forth in the appended claims. 

1. An elongated, thin strip article that is formed from corrosion resistant alloy comprising, in weight percent, about: C 0.03 max. Mn 1.0 max. Si 0.75 max. P 0.040 max. S 0.020 max. Cr 10.9-11.1 Ni 10.9-11.1 Mo 0.9-1.1 Ti 1.5-1.6 Al 0.25 max. Nb 0.7-0.8 Cu 1 max. B 0.010 max. N 0.030 max.

and the balance is iron and usual impurities, said elongated thin strip article having a room temperature tensile strength of at least about 280 ksi in the solution treated and age hardened condition.
 2. An elongated strip article as claimed in claim 1 wherein the strip has a thickness of about 0.02 to 0.16 inches.
 3. An elongated strip article as claimed in claim 1 wherein the alloy has an average grain size not greater than about ASTM 7-8 in major dimension.
 4. An elongated strip article as claimed in claim 1 which has a hardness of about 53-54 HRC.
 5. A method of making a thin strip article comprising the steps of casting a corrosion resistant alloy comprising, in weight percent, about C 0.03 max. Mn 1.0 max. Si 0.75 max. P 0.040 max. S 0.020 max. Cr 10.9-11.1 Ni 10.9-11.1 Mo 0.9-1.1 Ti 1.5-1.6 Al 0.25 max. Nb 0.7-0.8 Cu 1 max. B 0.010 max. N 0.030 max.

and the balance being iron and usual impurities to form an ingot; mechanically working said ingot to form an elongated strip material; and then heat treating said elongated strip material under conditions of time and temperature to provide an ultimate tensile strength of at least about 280 ksi at room temperature.
 6. A method as claimed in claim 5 wherein the step of heat treating the elongated strip material comprises the steps of: heating the elongated strip material at a temperature of about 1900-2000° F.; and then heating the elongated strip material at a temperature of about 900° F. to about 950° F.
 7. A method as claimed in claim 6 wherein the first heating step comprises heating the alloy at a temperature of about 1900-1950° F. and the method comprises the following steps between the heating steps: rapidly cooling the alloy to about −100° F.; and then holding the alloy at about −100° F. for a period of time to substantially completely transform any austenite in the alloy to martensite.
 8. A method as claimed in claim 5 wherein the step of mechanically working the ingot comprises the steps of: pressing the ingot to form a billet; and then hot rolling the billet to form the elongated strip material.
 9. A method as claimed in claim 5 wherein the step of mechanically working the ingot comprises hot rolling the ingot to form the elongated strip material.
 10. A method as claimed in claim 9 wherein the hot rolling step comprises heating the billet to about 1900-2250° F.
 11. A method of making a golf club head comprising the steps of casting a corrosion resistant alloy comprising, in weight percent, about C 0.03 max. Mn 1.0 max. Si 0.75 max. P 0.040 max. S 0.020 max. Cr 10.9-11.1 Ni 10.9-11.1 Mo 0.9-1.1 Ti 1.5-1.6 Al 0.25 max. Nb 0.7-0.8 Cu 1 max. B 0.010 max. N 0.030 max.

and the balance being iron and usual impurities to form an ingot; mechanically working said ingot to form an elongated strip material; heat treating said elongated strip material under conditions of time and temperature to improve the machinability and processability of the material; cutting said elongated strip material to form a faceplate for a golf club head; forming a golf club head body from a corrosion resistant precipitation hardenable steel alloy; bonding said faceplate to said golf club head body to form a golf club head assembly; and then heat treating said golf club head assembly under conditions of time and temperature to provide hardness and strength in the golf club head assembly and an ultimate tensile strength of at least about 280 ksi at room temperature in said faceplate.
 12. A method as claimed in claim 11 wherein the step of heat treating the golf club heat assembly comprises the steps of: heating the elongated strip material at a temperature of about 1900-2000° F.; and then heating the elongated strip material at a temperature of about 900° F. to about 950° F.
 13. A method as claimed in claim 12 wherein the first heating step comprises heating the golf club heat assembly at a temperature of about 1900-1950° F. and the method comprises the following steps between the heating steps: rapidly cooling the golf club head assembly to about −100° F.; and then holding the golf club head assembly at about −100° F. for a period of time to substantially completely transform any austenite in the alloy to martensite.
 14. A method as claimed in claim 11 wherein the step of mechanically working the ingot comprises the steps of pressing the ingot to form a billet; and then hot rolling the billet to form the elongated strip material.
 15. A method as claimed in claim 11 wherein the step of mechanically working the ingot comprises hot rolling the ingot to form the elongated strip material.
 16. A method as claimed in claim 15 wherein the hot rolling step comprises heating the billet to about 1900-2250° F.
 17. A method as claimed in claim 11 wherein the step of heat treating the elongated strip material comprises the step of overaging the strip material at about 1100-1350° F.
 18. A method as claimed in any of claims 11 to 13 wherein the step of mechanically working the ingot comprises the steps of: pressing the ingot to form a billet; hot rolling the billet to form the elongated strip material; and then cold rolling the elongated strip material to reduce its thickness to final or near final dimension.
 19. A method as claimed in any of claims 11 to 13 wherein the step of mechanically working the ingot comprises the steps of: hot rolling the ingot to form elongated strip material; and then cold rolling the elongated strip material to reduce its thickness to final or near final dimension.
 20. A method as claimed in claim 18 or claim 19 wherein the hot rolling step comprises heating the ingot or billet to about 1038-1232° C.
 21. A method as claimed in claim 19 wherein the hot rolling step comprises heating the ingot or billet to about 1038-1232° C. 